Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $240.49   11.501%   $268.1488   $268.15   $268.15   $268.10  
  Purchase #2 $207.51   5.832%   $219.612   $219.61   $219.60   $219.60  
  Purchase #3 $156.42   11.234%   $173.9922   $173.99   $174.00   $174.00  
  Purchase #4 $127.35   9.583%   $139.554   $139.55   $139.55   $139.60  
  Purchase #5 $211.58   6.838%   $226.0478   $226.05   $226.05   $226.00  
  Purchase #6 $197.35   3.392%   $204.0441   $204.04   $204.05   $204.00  
  Purchase #7 $147.61   4.113%   $153.6812   $153.68   $153.70   $153.70  
  7 purchase totals = $1,288.31       $1,385.0801   $1,385.07   $1,385.10   $1,385.00